It is a well known form of exercise to create a resistance to muscular contraction or elongation. Exercise producing resistance may be provided by free weights, i.e., barbells or plates attached to a bar, or machines utilizing, for example, weight stacks, compressed air, hydraulics, magnets, friction, springs, bending flexible rods, rotating fan blades, mechanical dampers or the users own body weight. A conventional exercise with free weights, for example, involves a xe2x80x9cpositivexe2x80x9d movement in which the muscle under training is contracting to lift a weight and a xe2x80x9cnegativexe2x80x9d movement in which that muscle is elongating to lower the weight. Many exercise machines emulate the exercise movements used in free weight training.
There are many disadvantages to exercising with both free weights and these conventional exercise machines. For instance, free weights are potentially hazardous without a partner to xe2x80x9cspotxe2x80x9d the user, and it is difficult and time consuming to adjust the amount of weight to be used in order to perform a different exercise or to accommodate another person of differing strength. Various exercise machines tend to be heavy and/or bulky and do not offer the intensity, range-of-movement and variety of movement of free weights. Also, both free weights and weight machines cannot be used in a gravity-free environment, such as encountered by astronauts.
An alternative form of exercise utilizes inertia to provide exercise-producing resistance. Such exercise is based on the principle that force is required to rotationally accelerate a mass, i.e., to increase or decrease the rotational velocity of a mass. An inertial exercise device has several advantages over both free weights and conventional exercise machines. Less bulk is required because the difficulty of the exercise depends not only on mass but also on the angular acceleration of mass. No partner is required as with free weights. Further, an inertial exercise device does not require gravity.
Existing exercise devices utilizing inertia, however, suffer from several disadvantages. Many such devices provide only a positive work exercise. Further, it is often difficult to vary the resistance of inertial exercises. Finally, unlike free weights or some exercise machines, existing inertia-based exercise devices have difficulty providing a constant resistance and/or constant speed of movement.
The present invention relates to an exercise apparatus and method in which exercise-producing resistance is provided by the inertia of a rotatable mass. One aspect of this invention employs a flywheel which is axially mounted to a rotatable axle. One end of a line is attached to the axle. In an initial position, a portion of the line is wrapped about a portion of the axle. A user applying a force to the unattached end of the line creates an accelerating torque on the axle, causing the axle to begin rotating and the line to begin unwrapping. As the user increases the force on the line, the axle and flywheel rotate with increasing velocity. When the line is completely unwrapped from the axle, inertia causes the axle to continue rotating in the same direction. This continued rotation of the axle causes the line to wrap about the axle in the opposite direction from the initial position of the line. The user then applies a force to the line to slow the rotation of the axle and decelerate the flywheel. The user applied force preferably stops the rotation of the flywheel and axle when a portion of the line is wrapped about a portion of the axle. In one embodiment, the line may wrap and unwrap around an axle with a gradually increasing diameter. Preferably, this causes the acceleration of the axle to be continuously changing.
Another aspect of this invention is an exercise apparatus with two axles which are interconnected with a synchronizing assembly such that both axles rotate. One end of a line is attached to the first axle. In an initial position, a portion of the line is wrapped about a portion of the first axle. A flywheel is axially mounted to the second axle. A user applying a force to the unattached end of the line creates an accelerating torque on the axle, causing the axle to begin rotating and the line to begin unwrapping. Due to the synchronizing assembly, the second axle also rotates, which causes the flywheel to rotate. When the line becomes completely unwrapped from the first axle, the inertia of the flywheel causes the second axle to continue rotating in the same direction and, hence, the first axle also continues to rotate in the same direction. Rotation of the first axle causes the line to wrap about the first axle in the opposite direction from the initial position of the line. The user then applies force to the line to slow the rotation of the first axle and, due to the synchronizing assembly, also the second axle, causing the rotational velocity of the flywheel to decrease. The user applied force preferably stops the rotation of the flywheel and axles when a portion of the line is wrapped about a portion of the first axle. In one embodiment, the line wraps and unwraps around an axle with a generally increasing diameter. In another embodiment, a generally constant force applied to the line results in a generally continuously changing acceleration of the axle.
Yet another aspect of this invention provides a rotatably mounted axle and a flywheel mounted to the axle. A linkage connects a grip to the axle. A force applied to the grip in a first direction causes the axle and flywheel to rotate in one direction. A force applied to the grip in a second direction causes the axle and flywheel to slow or stop rotating in that direction. A continued force in the second direction may cause the axle and flywheel to rotate in the opposite direction.
The present invention also relates to a method of creating resistance for exercising which utilizes the rotational inertia of a flywheel. The user exercises his or her muscles by exerting a force which alternately accelerates and decelerates a rotating flywheel. In one aspect of the invention, the user applies a positive work movement to the apparatus to increase the rotational velocity of the flywheel and a negative work movement to the apparatus to decrease the rotational velocity of the flywheel. The positive work movement creates a force which is translated into a torque. That torque is applied to the flywheel in a first direction to accelerate the flywheel. A negative work movement creates a second force which is translated into a second torque. The second torque is applied to the flywheel in a direction opposite the first direction. This causes the flywheel to decelerate.